Generally the present invention relates to phosphor compositions. More particularly, the present invention relates to off stoichiometric garnet phosphors having enhanced emissions in defined spectral regions compared to conventional garnet phosphors.
Light emitting diodes (LEDs) are semiconductor light emitters often used as a replacement for other light sources, such as incandescent lamps. The color of light produced by an LED is dependent on the type of semiconducting material used in its manufacture. Colored semiconductor light emitting devices, including light emitting diodes and lasers (both are generally referred to herein as LEDs), have been produced from Group III-V alloys such as gallium nitride (GaN). In the GaN-based LEDs, light is generally emitted in the UV and/or blue range of the electromagnetic spectrum.
In one technique of converting the light emitted from LEDs to useful light, the LED is coated or covered with a phosphor layer. Some phosphors emit radiation in the visible portion of the electromagnetic spectrum in response to excitation by electromagnetic radiation outside the visible range.
By interposing a phosphor excited by the radiation generated by the LED, light of different wavelengths in the visible range of the spectrum may be generated. Colored LEDs are often in demand to produce custom colors and higher luminosity.
In addition to colored LEDs, a combination of LED generated light and phosphor generated light may be used to produce white light. The most popular white LEDs consist of blue emitting GaInN chips. The blue emitting chips are coated with a phosphor that converts some of the blue radiation to a complimentary color, e.g. a yellow-green emission. Together, the blue and yellow-green radiation produces a white light. There are also white LEDs that utilize a UV emitting chip and a phosphor blend including red, green and blue emitting phosphors designed to convert the UV radiation to visible light.
Phosphor blends utilizing deep red phosphors are sometimes used to produce light sources having a high color rendering index (CRI). While effective, such phosphors may reabsorb emission from other phosphors that may be present in the illumination device. Thus, a need exists for a new phosphor having a red emission for use in LEDs displaying high quantum efficiency (QE) to produce both colored and white-light LEDs having a high CRI.
Another potential method to enhance the CRI of a lighting source using a blue or UV LED to excite a phosphor is to enhance the emission of the device in the blue-green region. Thus, a need exists for a phosphor having enhanced spectral output in this region when excited by blue or UV light.